Impeller suspension mechanism for heart pump

ABSTRACT

A centrifugal blood pump includes a housing that defines an inlet passage, a chamber, and an outlet passage. The pump includes an impeller rotatably positioned in the chamber to transfer blood from the inlet passage through the chamber and to the outlet passage and magnetic members embedded in the impeller such that the impeller and the magnetic members rotate together within the chamber. The pump includes a motor to control movement of the impeller in the chamber. The motor is adjacent the chamber and separated from the chamber by a partition member. The pump includes an inner annular magnetic member and an outer annular magnetic member embedded in a side of the housing opposite the partition member. A first net magnetic force between the inner annular magnetic member and the magnetic members exhibits greater attraction than a second net magnetic force between the outer annular member and the magnetic members.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is continuation of U.S. patent application Ser. No.15/042,685, filed Feb. 12, 2016 and entitled “IMPELLER SUSPENSIONMECHANISM FOR HEART PUMP,” which claims priority to U.S. ProvisionalApplication No. 62/115,741, filed Feb. 13, 2015 and entitled “IMPELLERSUSPENSION MECHANISM FOR HEART PUMP,” which are hereby incorporated byreference in their entirety, for all purposes, as if fully set forthherein.

BACKGROUND OF THE INVENTION

Conventional heart pumps utilize magnetic elements and/or hydrostaticbearings within a housing of the pump to compensate attractive forcesproduced by a stator motor to maintain an impeller of the pump in adesired position within a chamber of the pump. Such magnetic attractiveforces from the magnetic elements provide negative stiffness. Thisnegative stiffness increases as a distance between the magnetic elementswithin the housing and magnets on the impeller becomes shorter. Any tiltof the impeller will decrease a gap between the impeller and the wall ofthe chamber at an outer edge of the impeller. At low impeller speeds,hydrodynamic bearing forces are sufficient to maintain this gap.However, in conventional pump designs, at high speeds the impeller tendsto tilt, resulting in a decrease of a size of the gap near the outeredges of the impeller.

BRIEF SUMMARY OF THE INVENTION

In one aspect, a centrifugal blood pump is provided. The pump mayinclude a housing that defines an inlet passage, a chamber, and anoutlet passage. The pump may also include an impeller rotatablypositioned in the chamber to transfer blood from the inlet passagethrough the chamber and to the outlet passage. The impeller may includean inner portion and an outer portion. The pump may further include aplurality of impeller magnets embedded in the impeller such that theimpeller and the plurality of impeller magnets rotate together withinthe chamber. The plurality of impeller magnets may include an innerimpeller magnet and an outer impeller magnet relative to a central axisof the impeller. The pump may include a motor to control movement of theimpeller in the chamber. The motor may be positioned adjacent thechamber and separated from the chamber by a partition member. The pumpmay also include an inner annular magnetic member embedded in a wall ofthe housing opposite the partition member and an outer annular magneticmember embedded in the wall of the housing opposite the partitionmember. A first net magnetic force between the inner annular magneticmember and the inner impeller magnet may exhibit greater attraction thana second net magnetic force between the outer annular member and theouter impeller magnet.

In another aspect, a centrifugal blood pump may include a housing thatdefines an inlet passage, a chamber, and an outlet passage. The pump mayalso include an impeller rotatably positioned in the chamber to transferblood from the inlet passage through the chamber and to the outletpassage. The pump may further include a plurality of impeller magnetsembedded in the impeller such that the impeller and the plurality ofimpeller magnets rotate together within the chamber. The pump mayinclude a motor to control movement of the impeller in the chamber. Themotor may be positioned adjacent the chamber and separated from thechamber by a partition member. The pump may further include at least oneannular magnetic member embedded in a wall of the housing opposite thepartition member. A first net magnetic force between the at least oneannular magnetic member and a proximal portion the plurality of impellermagnets may exhibit greater attraction than a second net magnetic forcebetween the at least one annular magnetic member and a distal portion ofthe plurality of impeller magnets. The proximal portion and the distalportion may be relative to a central axis of the impeller.

In another aspect, a centrifugal blood pump may include a housing thatdefines an inlet passage, a chamber, and an outlet passage. The pump mayalso include an impeller rotatably positioned in the chamber to transferblood from the inlet passage through the chamber and to the outletpassage. The impeller may include an inner portion and an outer portionrelative to a central axis of the impeller. The pump may further includeat least one impeller magnet embedded in the impeller such that theimpeller and at least one magnetic member rotate together within thechamber. The pump may include a motor to control movement of theimpeller in the chamber. The motor may be positioned adjacent thechamber and separated from the chamber by a partition member. The pumpmay also include at least one annular magnetic member embedded in a sideof the housing opposite the partition member. A first force exhibited onthe inner portion may have a greater attraction than a second forceexhibited on the outer portion of the impeller. The first force and thesecond force may each result from interactions between the at least oneimpeller magnet and the at least one annular magnetic member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example centrifugal blood pump according to thedisclosure.

FIG. 2 shows the blood pump of FIG. 1 in an alternate view.

FIG. 3 shows a cross-section of the blood pump of FIG. 1.

FIG. 4 shows another cross-section of the blood pump of FIG. 1.

FIG. 5 shows yet another cross-section of the blood pump of FIG. 1.

FIG. 6 shows yet another cross-section of the blood pump of FIG. 1.

FIG. 7 shows yet another cross-section of the blood pump of FIG. 1.

FIG. 8 shows one embodiments of magnetic stabilization features of ablood pump according to embodiments.

FIG. 9 shows one embodiments of magnetic stabilization features of ablood pump according to embodiments.

FIG. 10 shows one embodiments of magnetic stabilization features of ablood pump according to embodiments.

FIG. 11 shows one embodiments of magnetic stabilization features of ablood pump according to embodiments.

FIG. 12 shows one embodiments of magnetic stabilization features of ablood pump according to embodiments.

FIG. 13 shows one embodiments of magnetic stabilization features of ablood pump according to embodiments.

FIG. 14 shows one embodiments of magnetic stabilization features of ablood pump according to embodiments.

FIG. 15 shows one embodiments of magnetic stabilization features of ablood pump according to embodiments.

DETAILED DESCRIPTION OF THE INVENTION

The ensuing description provides exemplary embodiments only, and is notintended to limit the scope, applicability or configuration of thedisclosure. Rather, the ensuing description of the exemplary embodimentswill provide those skilled in the art with an enabling description forimplementing one or more exemplary embodiments. It being understood thatvarious changes may be made in the function and arrangement of elementswithout departing from the spirit and scope of the invention as setforth herein.

Specific details are given in the following description to provide athorough understanding of the embodiments. However, it will beunderstood by one of ordinary skill in the art that the embodiments maybe practiced without these specific details. For example, with regard toany specific embodiment discussed herein, any one or more details may ormay not be present in all versions of that embodiment. Likewise, anydetail from one embodiment may or may not be present in any particularversion of another embodiment discussed herein. Additionally, well-knowncircuits, systems, processes, algorithms, structures, and techniques maybe shown without unnecessary detail in order to avoid obscuring theembodiments. The absence of discussion of any particular element withregard to any embodiment herein shall be construed to be an implicitcontemplation by the disclosure of the absence of that element in anyparticular version of that or any other embodiment discussed herein.

The present disclosure is directed to, among other things, minimizing orpreventing a decrease in gap size at high impeller speeds between theouter edge of the impeller and the inner wall of a chamber of a bloodpump. Some aspects of the disclosure are directed to reducing the riskof undesirable tilting of the impeller and/or improving the overallstability of the impeller during operation. Embodiments maintain anappropriately sized gap through all impeller speeds by decreasing thenet attractive magnetic force on an outer portion of the impeller, or byhaving a lower net attractive force on an outer portion of the impellerthan an inner portion. Although the feature or aspects of the presentdisclosure are not limited to a specific type of mechanical blood pump,an example of a blood pump in which embodiments of maintaining anappropriate gap size may be practiced is shown and described inconnection with FIGS. 1-7. As will be understood by one of skill fromthe description herein, some of the features described increase astabilizing force on the impeller over conventional non-contact pumpbearings, in various respects, along the tilt axis.

In FIGS. 1-7, an exemplary centrifugal blood pump is shown that includesa pump unit 1 that includes a housing 2 made of a nonmagnetic material.Housing 2 includes a cylindrical body portion 3, a cylindrical bloodinlet port 4 that extends from one end surface of body portion 3, and acylindrical blood outlet port 5 that extends from another end surface ofbody portion 3. Blood outlet port 5 extends in a tangential direction ofthe outer circumferential surface of body portion 3.

As shown in FIG. 2, a position of one or more annular shaped magneticmembers is shown. In some embodiments, pump unit 1 may include an innerannular magnetic member 30 and an outer annular magnetic member 32.Other embodiments may include one annular magnetic member or more thantwo annular magnetic members. The annular magnetic members 30 and 32 mayeach be formed from a single ring-shaped magnetic member, or may beformed from a number of magnetic members arranged in an annular pattern.

As shown in FIG. 3, a blood chamber 7 and a motor chamber 8 arepartitioned from each other by a dividing wall 6 within housing 2. Bloodchamber 7, as shown in FIGS. 3-4, includes a rotatable disc-shapedimpeller 10 having a through hole 10 a in a center thereof. Impeller 10includes two shrouds 11, 12 in an annular shape, and a plurality (e.g.,six) of vanes 13 formed between two shrouds 11 and 12. Shroud 11 isarranged on the blood inlet port 4 side, and shroud 12 is arranged onthe dividing wall 6 side. Shrouds 11, 12 and vanes 13 are made of anonmagnetic material.

A plurality (six in this case) of blood passages 14 are formed betweentwo shrouds 11 and 12 and are partitioned from one another by theplurality of vanes 13. As shown in FIG. 4, blood passage 14 is incommunication with through hole 10 a at the center of impeller 10, andextends with through hole 10 a of impeller 10 as a starting point to anouter circumference such that blood passage 14 gradually increases inwidth. In other words, each vane 13 is formed between two adjacent bloodpassages 14. In the first embodiment, the plurality of vanes 13 areprovided at regular angular intervals, and each has the same shape.Thus, the plurality of blood passages 14 are provided at regular angularintervals and has the same shape.

When impeller 10 is driven to rotate, blood that has flowed in throughblood inlet port 4 is delivered by centrifugal force from through hole10 a to an outer circumferential portion of impeller 10 via bloodpassages 14, and flows out through blood outlet port 5. It iscontemplated that the blood inlet port 4 may be configured and/orarranged to minimize or prevent the formation of thrombosis within(i.e., internal) the blood inlet port 4, and also to minimize turbulenceat a fluid interface between the blood inlet port 4 and the bloodchamber 7.

A plurality of permanent magnets may be embedded in shroud 11. Forexample, an inner magnet 15 and an outer magnet 16 may be included inshroud 11. One or more annular magnetic members may be embedded in aninner wall of blood chamber 7 facing shroud 11. For example, innerannular magnetic member 30 and outer annular magnetic member may beembedded in the inner wall. The annular magnetic members 30 and 32 maybe permanent magnets or may be electromagnetic elements. Either a softmagnetic element or a hard magnetic element may be used as the annularmagnetic members 30 and/or 32.

The annular magnetic members 30 and 32 may each be formed as a singlepermanent magnet or as a plurality of permanent magnets. If a singlepermanent magnet is provided, the permanent magnet is formed in anannular or ring shape. If a plurality of permanent magnets are provided,the plurality of permanent magnets may be arranged at regular angularintervals along the same circle. While described as annular magneticmembers, it will be appreciated that each of the magnetic membersdescribed herein may be formed from one or more magnets, and may be inany non-annular arrangement, such as other symmetrical shapes. In someembodiments, the inner annular magnetic member 30 may have a greater netattractive force with the inner magnet 15 than the net attractive forcebetween the outer annular magnetic member 32 and the outer magnet 16.Such a configuration may decrease the tilt of the impeller, especiallyat high impeller speeds, thus maintaining a size of the gap between theouter edge of the impeller and the housing wall.

As shown in FIG. 4, a plurality (e.g., nine) of permanent magnets 17 areembedded in shroud 12. The plurality of permanent magnets 17 arearranged with a gap therebetween at regular angular intervals along thesame circle such that magnetic polarities of adjacent permanent magnets17 are different from each other. In other words, permanent magnet 17having the N-pole toward motor chamber 8 and permanent magnet 17 havingthe S-pole toward motor chamber 8 are alternately arranged with a gaptherebetween at regular angular intervals along the same circle.

As shown in FIG. 3 and FIG. 7, a plurality (e.g., nine) of magneticelements 18 are provided in motor chamber 8. The plurality of magneticelements 18 are arranged at regular angular intervals along the samecircle to face the plurality of permanent magnets 17 in impeller 10. Abase end of each of the plurality of magnetic elements 18 is joined toone disc-shaped magnetic element 19. A coil 20 is wound around eachmagnetic element 18. In the direction of a central axis of impeller 10,the length of magnetic element 18 is shorter than that of coil 20. Thatis, when an axial length of magnetic element 18 is expressed as x and anaxial length of coil 20 is expressed as L relative to the surface ofdisc-shaped magnetic element 19, a relationship of 0<x<L is satisfied.

Referring back to FIG. 7, space for winding coil 20 is equally securedaround the plurality of magnetic elements 18, and surfaces facing eachother of every two adjacent magnetic elements 18 are providedsubstantially in parallel to each other. Thus, a large space for coils20 can be secured and turns of coils 20 can be increased. As a result,large torque for driving impeller 10 to rotate can be generated.Further, copper loss that occurs in coils 20 can be reduced, therebyenhancing energy efficiency when impeller 10 is driven to rotate. Theplurality of magnetic elements 18 may be formed in a cylindrical shape.In this case, a circumferential length of coils 20 can be minimized toreduce copper loss that occurs in coils 20, thereby enhancing energyefficiency when impeller 10 is driven to rotate.

An outline surface surrounding the plurality of magnetic elements 18 (acircle surrounding the peripheries of the plurality of magnetic elements18 in FIG. 7) may correspond to an outline surface surrounding theplurality of permanent magnets 17 (a circle surrounding the peripheriesof the plurality of magnetic elements 18 in FIG. 4), or the outlinesurface surrounding the plurality of magnetic elements 18 may be largerthan the outline surface surrounding the plurality of permanent magnets17. Further, it is preferable that magnetic element 18 be designed notto be magnetically saturated at maximum rating of pump 1 (a conditionwhere torque for driving impeller 10 to rotate becomes maximum).

Voltages are applied to nine coils 20 in a power distribution systemshifted by 120 degrees, for example. That is, nine coils 20 are dividedinto groups each including three coils. Voltages are applied to first tothird coils 20 of each group, respectively. To first coil 20, a positivevoltage is applied during a period of 0 to 120 degrees, 0 V is appliedduring a period of 120 to 180 degrees, a negative voltage is appliedduring a period of 180 to 300 degrees, and 0 V is applied during aperiod of 300 to 360 degrees. Accordingly, a tip surface of magneticelement 18 having first coil 20 wound therearound (end surface on theimpeller 10 side) becomes the N-pole during the period of 0 to 120degrees, and becomes the S-pole during the period of 180 to 300 degrees.A Voltage VV is delayed in phase from a voltage VU by 120 degrees, and avoltage VW is delayed in phase from voltage VV by 120 degrees. Thus,rotating magnetic field can be formed by applying voltages VU, VV, VW tofirst to third coils 20, respectively, so that impeller 10 can berotated by attractive force and repulsion force between the plurality ofmagnetic elements 18 and the plurality of permanent magnets 17 inimpeller 10.

When impeller 10 is rotating at a rated rotation speed, attractive forcebetween the magnetic elements 15 and 16 and the annular magnetic members30 and 32 and attractive force between the plurality of permanentmagnets 17 and the plurality of magnetic elements 18 are set to bebalanced with each other substantially around a center of a movablerange of impeller 10 in blood chamber 7. Thus, force acting on impeller10 due to the attractive force is very small throughout the movablerange of impeller 10. Consequently, frictional resistance duringrelative slide between impeller 10 and housing 2 which occurs whenimpeller 10 is activated to rotate can be reduced. In addition, asurface of impeller 10 and a surface of an inner wall of housing 2 arenot damaged (no projections and recesses in the surfaces) during therelative slide, and moreover, impeller 10 is readily levitated fromhousing 2 without contacting even when hydrodynamic force is smallduring low-speed rotation.

A number of grooves of hydrodynamic bearing 21 are formed in a surfaceof dividing wall X facing shroud 12 of impeller 10, and a number ofgrooves of hydrodynamic bearing 22 are formed in the inner wall of bloodchamber 7 facing shroud 11. When a rotation speed of impeller 10 becomeshigher than a prescribed rotation speed, a hydrodynamic bearing effectis produced between each of the grooves of hydrodynamic bearings 21 and22 and impeller 10. As a result, drag is generated on impeller 10 fromeach of the grooves of hydrodynamic bearings 21 and 22, causing impeller10 to rotate without contacting in blood chamber 7.

Specifically, as shown in FIG. 5, each of the grooves of hydrodynamicbearing 21 are formed with a size corresponding to shroud 12 of impeller10. Each groove of hydrodynamic bearing 21 is positioned with one end onan edge (circumference) of a circular portion slightly distant from acenter of dividing wall 6. Each groove extends from the edge spirally(in other words, in a curved manner) toward a portion near an outer edgeof dividing wall 6 such that the groove of the hydrodynamic bearing 21gradually increases in width. Each of the grooves of hydrodynamicbearing 21 has substantially the same shape, and the grooves arearranged at substantially regular intervals. Each groove of hydrodynamicbearing 21 includes a concave portion. Each groove may have a depth ofbetween about 0.005 to 0.400 mm. Between about 6 to 36 grooves may formhydrodynamic bearing 21.

In FIG. 5, ten grooves in an equiangular arrangement with respect to thecentral axis of impeller 10 form hydrodynamic bearing 21. Since thegrooves of hydrodynamic bearing 21 have a so-called inward spiral grooveshape, clockwise rotation of impeller 10 causes an increase in fluidpressure from an outer diameter portion toward an inner diameter portionof the grooves for hydrodynamic bearing 21. As a result, a repulsiveforce that acts as a hydrodynamic force is generated between impeller 10and dividing wall 6.

In some embodiments, alternatively, or in addition to, providing groovesfor hydrodynamic bearing 21 in dividing wall 6, grooves for hydrodynamicbearing 21 may be provided in a surface of shroud 12 of impeller 10. Thehydrodynamic bearing effect produced between impeller 10 and the groovesof hydrodynamic bearing 21, causes impeller 10 to move away fromdividing wall 6 and to rotate without contacting the dividing wall 6.Accordingly, a blood flow path is secured between impeller 10 anddividing wall 6, thus preventing occurrence of blood accumulationtherebetween and the resultant thrombus. Further, in a normal state, thegrooves of hydrodynamic bearing 21 perform a stirring function betweenimpeller 10 and dividing wall 6, thus preventing occurrence of partialblood accumulation therebetween.

It is preferable that a corner portion of each of grooves forhydrodynamic bearing 21 be rounded to have R of at least 0.05 mm. As aresult, occurrence of hemolysis can further be reduced.

As with the grooves of hydrodynamic bearing 21, as shown in FIG. 6, thegrooves of hydrodynamic bearing 22 are each formed with a sizecorresponding to shroud 11 of impeller 10. Each groove of hydrodynamicbearing 22 has one end on an edge (circumference) of a circular portionslightly distant from a center of the inner wall of blood chamber 7. Thegroove extends spirally (in other words, in a curved manner) toward aportion near an outer edge of the inner wall of blood chamber 7 suchthat the groove gradually increases in width. Each of the grooves hassubstantially the same shape. The grooves are arranged at substantiallyregular intervals. Each groove of hydrodynamic bearing 22 includes aconcave portion. Each groove may have a depth of between about 0.005 to0.4 mm. It is preferable that about 6 to 36 grooves form hydrodynamicbearing 22. In FIG. 6, ten grooves forming hydrodynamic bearing 22 areequiangularly arranged with respect to the central axis of impeller 10.

Alternatively, or in addition to, providing the grooves of hydrodynamicbearing 22 in the inner wall of blood chamber 7, the grooves ofhydrodynamic bearing 22 may be provided in a surface of shroud 11 ofimpeller 10. It is preferable that a corner portion of each of groovesof hydrodynamic bearing 22 be rounded to have R of at least 0.05 mm. Asa result, occurrence of hemolysis can further be reduced

The hydrodynamic bearing effect produced between impeller 10 and thegrooves for hydrodynamic bearing 22 causes impeller 10 to move away fromthe inner wall of blood chamber 7 and rotates without contacting theinner wall. In addition, when pump unit 1 is subjected to externalimpact or when the hydrodynamic force generated by hydrodynamic bearing21 becomes excessive, impeller 10 can be prevented from being in closecontact with the inner wall of blood chamber 7. The hydrodynamic forcegenerated by hydrodynamic bearing 21 may be different from thehydrodynamic force generated by hydrodynamic bearing 22.

It is preferable that impeller 10 rotate in a state where a gap betweenshroud 12 of impeller 10 and dividing wall 6 is substantially equal to agap between shroud 11 of impeller 10 and the inner wall of blood chamber7. If one of the gaps becomes narrower due to serious disturbance suchas fluid force acting on impeller 10, it is preferable that grooves ofhydrodynamic bearing 21 and 22 have different shapes so that thehydrodynamic force generated by the hydrodynamic bearing on the narrowerside becomes higher than the hydrodynamic force generated by the otherhydrodynamic bearing to make the gaps substantially equal to each other.

While each groove of hydrodynamic bearings 21 and 22 has the inwardspiral groove shape shown in FIGS. 5-6, grooves having another shape maybe used. Nevertheless, for blood circulation, it is preferable to employgrooves having the inward spiral groove shape, which allows for a smoothflow of blood.

As mentioned above, it is contemplated that the blood inlet port 4 maybe configured and/or arranged to minimize or prevent the formation ofthrombosis within (i.e., internal) the blood inlet port 4, and also tominimize turbulence at a fluid interface between the blood inlet port 4and the blood chamber 7. In general, it is contemplated that thrombosisformation may occur due to a vortex forming in or within one or both ofblood inlet port 4 and the blood chamber 7 in a location near oradjacent blood inlet port 4, and/or due to stress or forces imparted onblood as it transitions into a spinning motion once it reaches theimpeller 10.

FIGS. 8-15 depict embodiments of pumps using one or more annularmagnetic members of a magnetic suspension system to maintain a size of agap between an impeller and a chamber wall of a housing at high impellerspeeds. Theses pumps may be configured as those described in FIGS. 1-7above. The annular magnetic members may correspond to the annularmagnetic members 30 and 32 described herein. The magnetic suspensionsystems are often made up of magnetic elements within the impeller,annular magnetic members embedded within a housing of the pump, a statormotor, and/or hydrostatic bearings formed in the housing. Embodimentsmaintain this gap size by producing a lower net attractive force at anouter or distal portion of the impeller than at an inner or proximalportion of the impeller. In some embodiments this net attractive forcerelationship is achieved by decreasing the attractive force at the outerportion or by producing a repulsive force at the outer portion. Otherembodiments achieve the greater inner attractive force by increasing theattractive force at the inner portion of the impeller. In otherembodiments, the gap may be maintained by using electromagnets as theannular magnetic members and utilizing active magnetic control to adjustthe magnetic forces as impeller speeds and/or gap size change.Alternative methods of increasing and/or maintaining the gap size athigh impeller speeds may also include increasing the gap between themotor stator and the motor magnet, although his may decrease theefficiency of the motor. It will be appreciated that combinations of thetechniques described herein may be used to further adjust and/ormaintain the gap size.

FIGS. 8 and 9 depict systems that decrease the outer annular magneticmember's magnetic force to create a greater net magnetic attraction atthe inner annular magnetic member. In FIG. 8, a pump 800 having ahousing 802 is shown. An impeller 804 is shown having a plurality ofmagnetic elements embedded therein. The impeller is configured to rotatewithin the housing 802. Here, an inner magnetic element 806 and an outermagnetic element 808 are embedded within impeller 804. One or moreannular magnetic members may be embedded within housing 802. Forexample, an inner annular magnetic member 810 and an outer annularmagnetic member 812 are embedded within a side wall of the housing 802.As shown here, by making a distance between the inner annular magneticmember 810 and inner magnetic element 806 less than a distance betweenouter annular magnetic member 812 and outer magnetic element 808, thenet attractive force along the outer edge of impeller 802 may bedecreased and/or made lower than the net attractive force at an innerportion of the impeller 802. This lessened attractive force results in areduction of negative stiffness at the outer annular magnetic member 812and an increase in the gap between the impeller 802 and the inner wallof the housing 804. Making the distance between the inner magnetssmaller than the distance between the outer magnets can be achieved bymoving the inner annular magnetic member 810 closer to the impeller, bymoving the outer annular magnetic member 812 away from the impeller,and/or by a combination of both.

In some embodiments, making the distance between the inner magnetssmaller than the distance between the outer magnets can be achieved bychanging a position of the inner magnet and/or the outer magnet relativeto the impeller as shown in FIG. 9. For example, a pump 900 may have ahousing 904 and an impeller 906 such as described in FIG. 8. An innermagnet 906 of the impeller 902 may be moved closer to an inner annularmagnetic member 910 within the housing 904 and/or an outer magnet 908may be moved away from an outer annular magnetic member 912. In someembodiments, one or more of both the housing magnetic members 810 and812 and the impeller magnetic elements 806 and 808 may be positioned tocreate the larger distance between the outer magnets than the innermagnets. In some embodiments, the net force difference between the innerand outer portions of the impeller may be attained by decreasing theattractive force at the outer annular magnetic member, such as byreducing the magnet size and/or otherwise reducing the strength of theouter annular magnetic member 912.

FIGS. 10 and 11 depict embodiments of pumps that increase a magneticforce of an inner annular magnetic member and decrease or eliminate amagnetic force of an outer annular magnetic member. For example, in FIG.10, a pump 1000 is shown having an impeller 1002, housing 1004, an innermagnetic element 1006, and an outer magnetic element 1008 as describedabove with regard to FIG. 8. Pump 1000 may include an inner annularmagnetic member 1010 having a net magnetic attraction with the innermagnetic element 1006 that is greater than a net magnetic attractionbetween an outer annular magnetic member 1012 and the outer magneticelement 1008. In pump 1000, this is done by increasing the magneticforce of the inner annular magnetic member 1010 in combination withreducing the magnetic force of the outer annular magnetic member 1012and/or by increasing the distance between the outer annular magneticmember 1012 and the outer magnetic element 1008. The increase inmagnetic force of the inner annular magnetic member may be realized byincreasing the magnet volume and/or by using a stronger magnet. In someembodiments, the magnetic force of the inner annular magnetic member1010 may be increased sufficiently such that the outer annular magneticmember 1012 and/or outer magnetic element 1008 may be eliminated. Forexample, FIG. 11 shows a pump 1100 having only a strong inner annularmagnetic member 1110 and an inner magnetic element 1106.

In some embodiments, the gap between the impeller and the housing may bemaintained by increasing the attractive force of the inner annularmagnetic member while using an opposite polarity magnet as the outerannular magnetic member to create a repulsive force on the outer edge ofthe impeller and to increase the impeller suspension stiffness. Forexample, FIG. 12 shows a pump 1200 having an inner annular magneticmember 1210 having a sufficiently high attractive magnetic force and anouter annular magnetic member 1212 that has a polarity relative to anouter magnetic element 1208 to create a repulsive force that serves tomaintain the gap size, even at high impeller speeds.

FIG. 13 shows one embodiment of a pump 1300 where a diameter of an outerannular magnetic member 1312 is increased to be larger than a diameterof an outer magnetic element 1308 on an impeller 1302 and/or to extendradially beyond at least a portion of the outer magnetic element 1308.The outer annular magnetic member 1312 also has a polarity selected tocreate a net repulsive force with the outer magnetic element 1308. Whenthe outer annular magnetic member 1312 extends beyond at least a portionof the outer magnetic element 1308, the repulsive force has a forcecomponent toward the rotational axis of the impeller 1302, whichincreases the radial stiffness. The impeller rotation center shiftstoward an outlet side of pump 1300 when the flow rate is high. Therepulsive force of the rotational axis direction increases as theimpeller is pushed toward the outlet side, compensating against pumppressure distribution due to the high flow rate. Thus, the repulsiveforce produce by the outer annular magnetic member 1312 helps maintainthe impeller position, and thus gap size, as impeller speeds increase.

In some embodiments, reduction of a diameter of an inner annularmagnetic member may be used in conjunction with increasing a diameter ofan outer annular magnetic member, resulting in an increase in the radialstiffness of the magnetic suspension system of the pump. For example,FIG. 14 shows a pump 1400 having an outer annular magnetic member 1412of increased diameter and an inner magnetic member 1410 having a reduceddiameter. By reducing the diameter of the inner annular magnetic member1410 such that the inner annular magnetic member 1410 is positioned atleast partially inward of the inner magnetic element 1406, a thicknessof a pump housing 1404 may be reduced by putting an inner annularmagnetic member 1410 of increased size within dead space of a pumpinflow conduit 1414. This positioning results in an increase in thenegative stiffness of the magnetic suspension system. The radialcomponent of the repulsive force of the outer annular magnetic membermaintains the impeller radial stiffness as the position of the innerannular magnetic member 1410 increases the negative stiffness.Additionally, the inward position of the inner annular magnetic member1410 increases the magnetic resistance while reducing the magnetic flux,and thus, the net attractive force acting on the impeller 1402. Therepulsive force of the outer annular magnetic member 1412 helpscompensate for the reduction of attractive force of the inner annularmagnetic member 1410 to maintain the gap size between the housing 1404and the impeller 1402.

In some embodiments, a ferromagnetic ring, such as a steel ring, may bepositioned between an inner annular magnetic member and an innermagnetic element when the inner annular magnetic member has a diameterpositioned inward of an inner magnetic element on an impeller. FIG. 15shows a pump 1500 having an outer annular magnetic member 1512 extendingradially beyond an outer magnetic element 1508 and an inner annularmagnetic member 1510 positioned inward of an inner magnetic element1506. Pump 1500 also includes a ferromagnetic ring 1516 positionedbetween inner annular magnetic member 1510 and inner magnetic element1506. The ring 1516 skews the magnetic flux such that the attractiveforce from the inner annular magnetic member 1510 is better directed toact upon the inner magnetic element 1506.

The invention has now been described in detail for the purposes ofclarity and understanding. However, it will be appreciated that certainchanges and modifications may be practiced within the scope of thedisclosure.

1. A blood pump comprising: an impeller disposed within a housing,wherein the impeller comprises an inner magnet and an outer magnetrelative to an axis of the impeller; and an inner annular magneticmember and an outer annular magnetic member disposed in a wall of thehousing relative to the axis of the impeller, wherein: the inner annularmagnetic member attracts the inner magnet; the outer annular magneticmember repels the outer magnet; and the outer annular magnetic memberextends radially beyond the outer magnet.
 2. The blood pump of claim 1,wherein: a distance between the outer magnet and the outer annularmagnetic member is greater than a distance between the inner magnet andthe inner annular magnetic member.
 3. The blood pump of claim 1,wherein: the inner annular magnetic member produces a greater magneticforce than the outer annular magnetic member.
 4. (canceled)
 5. The bloodpump of claim 1, wherein: at least a portion of the inner annularmagnetic member extends radially inward of the inner magnet.
 6. Theblood pump of claim 1, further comprising: a ferromagnetic ring disposedbetween the inner annular magnetic member and the inner magnet. 7.(canceled)
 8. The blood pump of claim 1, wherein: at least one of theinner annular magnetic member or the outer annular magnetic membercomprises an electromagnet.
 9. A blood pump comprising: an impellerdisposed within a housing, wherein the impeller comprises a plurality ofmagnets; and at least one annular magnetic member disposed in a wall ofthe housing, wherein: the at least one annular magnetic member attractsa first portion of the plurality of magnets proximate to an axis of theimpeller; the at least one annular magnetic member repels a secondportion of the plurality of magnets distal to the axis of the impeller;and the at least one annular magnetic member extends radially beyond theplurality of magnets.
 10. The blood pump of claim 9, wherein: theplurality of magnets comprises an inner magnet and an outer magnetrelative to an axis of the impeller.
 11. (canceled)
 12. The blood pumpof claim 9, wherein: the at least one annular magnetic member comprisesan inner annular magnetic member and an outer annular magnetic memberrelative to an axis of the impeller.
 13. The blood pump of claim 9,wherein: at least a portion of the at least one annular magnetic memberextends radially beyond the plurality of magnets.
 14. The blood pump ofclaim 9, wherein: at least a portion of the at least one annularmagnetic member extends radially inward of the plurality of magnets. 15.The blood pump of claim 9, further comprising: a ferromagnetic ringdisposed between the at least one annular magnetic member and theplurality of magnets.
 16. A blood pump comprising: an impeller disposedwithin a housing, wherein the impeller comprises a inner portion and anouter portion relative to an axis of the impeller; and at least oneannular magnetic member disposed in a wall of the housing, wherein: theat least one annular magnetic member attracts the inner portion of theimpeller; the at least one annular magnetic member repels the outerportion of the impeller; and the at least one annular magnetic memberextends radially beyond an outermost magnet of a plurality of magnetswithin the impeller.
 17. The blood pump of claim 16, wherein: the innerportion of the impeller comprises an inner magnet.
 18. The blood pump ofclaim 17, wherein: at least a portion of the at least one annularmagnetic member extends radially inward of the inner magnet. 19.(canceled)
 20. The blood pump of claim 16, further comprising: aferromagnetic ring disposed between the at least one annular magneticmember and the impeller.
 21. The blood pump of claim 9, wherein: the atleast one annular magnetic member comprises an inner annular magneticmember and an outer annular magnetic member relative to the axis of theimpeller; and a distance between the second portion of the plurality ofmagnets and the outer annular magnetic member is greater than a distancebetween the first portion of the plurality of magnets and the innerannular magnetic member.
 22. The blood pump of claim 9, wherein: the atleast one annular magnetic member comprises an inner annular magneticmember and an outer annular magnetic member relative to the axis of theimpeller; the inner annular magnetic member produces a greater magneticforce than the outer annular magnetic member.
 23. The blood pump ofclaim 9, wherein: the at least one annular magnetic member comprises anelectromagnet.
 24. The blood pump of claim 16, wherein: the at least oneannular magnetic member comprises an inner annular magnetic member andan outer annular magnetic member relative to the axis of the impeller;and a distance between the second portion of the plurality of magnetsand the outer annular magnetic member is greater than a distance betweenthe first portion of the plurality of magnets and the inner annularmagnetic member.
 25. The blood pump of claim 16, wherein: the at leastone annular magnetic member comprises an inner annular magnetic memberand an outer annular magnetic member relative to the axis of theimpeller; the inner annular magnetic member produces a greater magneticforce than the outer annular magnetic member.